Change starting frame of motion tracks
It sounds like you want to use blender's Video Sequence Editor.

http://wiki.blender.org/index.php/Doc:2.6/Manual/Sequencer/Usage

You will create a Movie or Image strip from your source clip.  You will then drag it to the right to open up some time at the beginning.  You can then add a strip for the added frames (whether they are an image sequence, movie clip, title card image, or solid color) in that space.